* Rebel lawmakers want referendum on UK leaving European Union
* Cameron seeks to shift focus on fixing euro zone crisis
* Vote is non-binding; seen as test of Cameron's authority
By Peter Griffiths
LONDON, Oct 24 British Prime Minister David Cameron faces the biggest rebellion of his premiership on Monday when parliament debates calls for a referendum on Britain's membership of the European Union.
Although the vote in parliament carries no legal weight, it is being seen as a test of the Conservative Party leader's authority and risks raising tensions within his ruling coalition with the pro-Europe Liberal Democrats.
Cameron, who opposes a public vote on Britain's EU membership, has sought to shift attention onto helping to solve the euro zone's debt crisis rather than debating London's often fractious links with Europe.
"This is the right time to sort out Europe's problems, sort out the euro zone problem," Cameron said on Sunday before scrapping plans to visit Japan and New Zealand so that he could attend a crucial European meeting on Wednesday.
His supporters accused "eurosceptics" in their party of distracting attention from the most important issues facing Britain and Europe -- Europe's crisis and weak global growth.
"That is the high drama at the moment," pro-European former Conservative minister Malcolm Rifkind told the BBC. "For us to be involved in this inward navel-gazing at this moment...is a massive distraction."
With the support of his junior coalition partner, the Liberal Democrats, and the main opposition Labour Party, Cameron is virtually assured of defeating the rebels. However, a bigger than expected revolt would raise questions about his authority.
Cameron is eager to regain the initiative after the resignation earlier this month of his former defence minister Liam Fox in a row over his links with a businessman. The government has also come under fire over its plans for to restore economic growth after a year of stagnation.
Despite the largely symbolic nature of the EU vote, Cameron appears to be taking no chances. He has imposed the toughest voting orders on his members of parliament. Known as a "three-line whip", lawmakers who defy the instruction to back the government will be effectively expelled from the party.
A poll for the Mail on Sunday newspaper found 61 percent of Britons want an EU referendum, while half wanted the government to renegotiate the terms of Britain's membership to focus on trade. However, only 34 percent wanted to leave the EU, compared to 44 who wanted to stay and 22 percent who did not know.
Eurosceptics on the right of Cameron's Conservatives are keen to use the euro zone's financial crisis to renegotiate London's ties with the EU. .
But those loyal to Cameron don't want to resurrect a debate that weakened former Conservative prime ministers Margaret Thatcher and John Major.
Around 70 of the more than 300 Conservative lawmakers are expected to vote against Cameron on Monday. Labour and the Lib Dems will tell members to vote with Cameron.
The Lib Dems said the vote would have little impact on the coalition, formed in May 2010 after an inconclusive election result that ended 13 years of Labour rule.
"A vote on something that doesn't bind government policy, where the government...has a clear line on it, and Labour don't support it: I don't see where the threat to the government is," a Lib Dem source told Reuters.